The present invention relates to a method and to a device for sensing low levels of iodine in an aqueous solution by using an extraction procedure whereby iodine from the aqueous solution is extracted into a substantially water-insoluble organic phase, and testing the color of the organic phase using optical absorption techniques.
It is a generally recognized principle that water must be effectively treated before it can be utilized in swimming pools, hot tubs and spas, particularly when the pools, etc. are used by segments of the general public. Swimming pools, hot tubs and spas are highly susceptible to rapid micro-organism growth and that they can rapidly become extremely hazardous to users thereof unless the water is effectively and continuously treated against micro-organisms.
One of the most widely recognized methods of treating water against micro-organisms to render the water safe for human consumption and/or use in swimming pools, spas, etc. is to add chlorine (normally in the form of a hypochlorite salt or chlorine gas) to the water. However, chlorine has been found to have an unpleasant or objectionable odor and can cause skin irritations and serious eye irritations to users of pools, spas, etc, an effect which is particularly noticeable in indoor swimming pools, hot tubs and spas. The use of chlorine can also lead to the formation of chloramines. Further, chlorine is sensitive to organic soils.
Due to the objectionable physical properties of chlorine a number of alternate water treatment systems have been developed in recent years, including the use of bromine and/or iodine.
It is known that iodine may be effectively used in small concentrations to impart desirable antimicrobial activity for various applications. For instance, U.S. Pat. No. 2,759,869, U.S. Pat. No. 3,029,183, U.S. Pat. No. 3,650,965, U.S. Pat. No. 3,525,696 and U.S. Pat. No. 3,150,096 all disclose aqueous liquid or said iodine use dilution compositions for various uses.
Further, it is known that iodine may be used in small concentrations to disinfect pools, hot tubs, spas and the like, and is typically formed by mixing oxidizable halide salts with an oxidizing agent. Active oxidizers include hydrogen peroxide, hypochlorite, peracid, chlorine dioxide, chlorate, chlorite, iodophors, and so forth. The iodide salt and oxidant may be mixed with a compound which is capable of forming a complex in order to improve the solubility of the iodine. An example of one such process is described in U.S. Pat. No. 5,130,033. Iodine may exist in the water as Ixe2x88x92, I2 and I3xe2x88x92. U.S. Pat. No. 4,946,673 discusses the use of germicidal iodine. It is the I2 species which act effectively against microbes.
These sanitizing systems must, however, be maintained at proper levels. Too much iodine, for instance, can result in an aesthetically objectionable color in the water. Too little iodine can result in the rapid growth of micro-organisms which, when once established, can rapidly propagate to unsafe levels. In order to maintain the iodine at proper levels, it is therefore necessary to have an easy and effective means of monitoring the concentration of iodine in the water. This can be a problem due to the low concentration of iodine employed.
Iodine is typically employed at concentrations of a few parts per million or less. For instance, U.S. Pat. No. 3,215,627 discloses a method for use in the disinfection of swimming pools. The range of free molecular iodine that is generated according to the method of the ""627 patent is between 0.2 and 0.4 ppm. U.S. Pat. No. 3,232,869 describes a method for purifying and disinfecting aqueous liquids with free molecular iodine wherein the iodine is provided by quantitatively oxidizing iodide ion into free molecular iodine with persulfates at a pH between 7 and 8. The patent requires the use of a stoichiometric amount of either iodide or persulfate to yield a free iodine concentration of 0.1 to 1.0 ppm of free molecular iodine. It is important that the concentration be maintained within its optimal use concentration range. However, due to the extremely low concentration levels it can be difficult to accurately detect its presence.
One option for detecting iodine is the oxidation-reduction potential (ORP) sensor found in U.S. Pat. No. 4,752,740. There are a couple of disadvantages to using this method, however. One disadvantage is that, because it depends on the ratio of an oxidized species over a reduced species, it requires the detection of more than one species. Consequently, this method is not unique to the species that actually kills the bacteria, for example the iodine species, but rather the measurement of the iodine species is embedded in the ratio. Furthermore, this method is susceptible to changes in pH. Its usefulness is therefore limited when employed in swimming pools, spas, hot tubs, etc.
Another method that may be used is the hand titration method in which thiosulfate is used to manually titrate the aqueous solution. Iodine is readily reduced by thiosulfate to iodide. The end point is indicated by the disappearance of the distinct blue color of the starch-iodine complex. This type of method is usually supplied as a test kit in which batches of water are tested, rather than a continuous monitoring system. Titration of iodine is discussed in U.S. Pat. No. 4,946,673. Automation of this procedure for continuous monitoring capabilities is complicated and expensive.
Another method is the optical absorption of the aqueous solution directly. However, this method is highly susceptible to low signal and high noise.
Each of these methods lacks the sensitivity required for accurately detecting low levels of iodine in the range of fractions of a part per million to a few parts per million.
The present invention relates to a novel process for the detection of free iodine in pools, spas, hot tubs and the like that is easier to use, is specific to the free iodine concentration, and that is not susceptible to the presence of other species and to pH changes.
The present invention relates to a process whereby low levels of iodine may be easily and readily detected. The iodine is extracted from an aqueous environment, for example a chemically treated pool, into a substantially water-insoluble organic phase whereby the iodine concentration is determined through the use of optical absorption.
In one aspect, the present invention relates to a novel method of sensing low levels of iodine in an aqueous solution comprising the steps of providing a substantially water-insoluble liquid organic phase trapped in a container by its low specific gravity and contacting the aqueous solution with the substantially water-insoluble liquid organic phase thereby distributing iodine between both the aqueous phase and the substantially water-insoluble organic phase. The contacting step may be accomplished by feeding the aqueous solution into the substantially water-insoluble organic phase. The water is subsequently separated through the natural forces of gravity, and by the fact that it is immiscible with the organic phase. The water may then be flowed into a waste stream, or optionally recycled back into its point of origination, i.e. a pool, spa, or hot tub, for instance. The container holding the substantially water-insoluble organic phase is transmissive to light at a wavelength absorbed by iodine in the substantially water-insoluble organic phase, allowing the amount of iodine in the substantially water-insoluble organic phase to be quantified by optical absorption. The amount of iodine in the aqueous phase can then be calculated using a known distribution coefficient or the ratio of iodine in the organic phase to iodine in the aqueous phase.
The present invention may be incorporated into a system wherein it is a continuous method of sensing iodine, or alternatively, the present invention can be used in a batch mode for detecting the amount of iodine.
A batch method finds use in instances where a composition, e.g. a concentrate, is being diluted for use and one wishes to determine the concentration of the diluted solution. A batch is also useful where the body of water from which the reading is taken is relatively small, i.e. less than 20 gallons, for instance.
In another aspect, the present invention relates to a device for continuously analyzing low levels of an iodine complex in an aqueous solution such as for a pool, spa or the like, the device comprising a container that is transmissive to light at a wavelength absorbed by iodine in the substantially water-insoluble organic phase; a substantially water-insoluble liquid organic phase in the container, the container configured in such a manner that the organic phase is above the aqueous phase in the container; a means for providing a stream of the aqueous solution to be analyzed into the organic phase; a photo detector for continuously measuring the optical absorption of said liquid organic phase at about 480 to about 560 nm wavelength; and an exiting means for the aqueous solution.
In another aspect, the present invention relates to a method of determining the concentration of a cleaning, bleaching or sanitizing composition after dilution with an aqueous liquid. This involves adding to the composition, a known amount of an iodide tracer, contacting the diluted composition with an aqueous solution comprising a sufficient amount of an oxidative compound thereby converting said iodide to iodine, contacting the iodine-containing aqueous solution with a water-insoluble liquid organic phase thereby extracting said iodine into said liquid organic phase. The concentration of iodine in the organic phase can then be measured using an optical absorption device, and the concentration of iodine can be equated with the concentration of iodide and the concentration of the diluted solution thus determined.
In yet another aspect of the invention, low levels of an oxidant can be detected by adding iodide ion to the aqueous solution, and the iodine thus formed can be determined in the same manner.